A number of efforts have been made to develop servo steering mechanisms associated with a joystick servo steering concept. A steering system was developed in the late nineteen-sixties that could make a vehicle automatically follow an antenna cable buried in the road. This system used an electronic proportional and derivative controller which regulated a hydraulic steering valve to turn the front wheels. A joystick steering system for a van was later developed that used a computer to automatically decrease the steering gain in proportion to the square of the vehicle speed in order to make the van safe to drive at higher speeds. The system was reported to be acceptable for use with test drivers. Recently, hydraulically powered joystick systems have been designed specifically for handicapped drivers. One joystick steering system (now marketed as the EMC Digidrive) uses an electric stepper motor to turn the steering wheel instead of regulating a power steering hydraulic valve. This system has a joystick input that decreases gain sensitivity with speed and steering wheel angle. All of these systems faced the common problem of having to compensate for steering gain when a vehicle travels at high speeds. These systems also involve a driver directly commanding the front wheel turn angle using a joystick.